The present invention relates to apparatus and a method for soldering/desoldering circuit components from a pc assembly. While the hot air rework tool (HART) has general applicability to any soldering/desoldering situation, its greatest advantage to date has been in "field rework" situations requiring the removal/installation of individual components (i.e., DIP's flatpacks, SSI, MSI and LSI integrated circuits) from a multilayer pc assembly at a customer site. For situations having multilayer pc assemblies of relatively few layers and/or components with relatively few pins, standard direct contact, resistance heating techniques can be used; but as the number of layers and pin counts increase so does the difficulty of the removal/installation operation. Primarily troublesome is the attendant heat sinking or spreading effect of the pc assembly, which effect requires higher heats. The higher heats in turn can damage the pc assembly by causing "measling" or delamination of the layers and/or the components.
While many devices exist that facilitate the soldering/desoldering operation, from wave soldering to direct contact heat transfer devices, some of which further have suction means for removing molten solder and extractor means for holding a component and facilitating its removal or insertion, none of these devices have proven to be cost effective or amenable to the "field rework" situation, especially for relatively thick multilayer pc assemblies. Prior to the development of the HART, components were generally removed using soldering irons and vacuum solder "gobblers." The process was relatively tedious though and required a variety of attachments to accomodate the various size packages and pin configurations encountered on the high density, multilayer pc assemblies.
The HART and method described herein however uses hot air as the primary heat transfer media and is adjustable to accomodate various size pc assemblies and components. The HART can heat either or both of the localized upper and lower surfaces of the pc assembly in the proximity of the desired component in either a concentrated or diffused manner, thereby creating a more uniform heat exchange environment which overcomes the heat spreading effects of the pc assembly. The HART also does away with the necessity of a solder suction device in that the air flow can more uniformly maintain the temperature of the solder in all the vias associated with a component so that all the pins can be inserted or removed without encountering any cold vias, which vias will not permit the component pin to be inserted or removed.
The present soldering/desoldering method is further improved by the application of a heat sensitive lacquer to the component or localized area during the solder/desoldering operation, which lacquer will melt at a specific temperature and thus indicate that the component can be removed or a new component inserted.